It is known that many oxygen sensitive products, including food products such as meat and cheese, smoked and processed luncheon meats, as well as non-food products such as electronic components, pharmaceuticals, and medical products, deteriorate in the presence of oxygen. Both the color and the flavor of foods can be adversely affected. The oxidation of lipids within the food product can result in the development of rancidity. These products benefit from the use of oxygen scavengers in their packaging.
One particular oxygen scavenger that has proved useful commercially is poly(ethylene/methyl acrylate/cyclohexene methyl acrylate) (abbreviated as EMCM). Although EMCM containing oxygen scavenging films have excellent cold seal strength, an EMCM layer tends to delaminate from adjacent layers at temperatures of 100 to 150° C. These temperatures are typical of those encountered during, or immediately after, heat-sealing of the film to itself or another material. Delamination can occur in packaging applications where vertically formed and filled packages are loaded before the heat seals are able to cool substantially. Due to poor interlayer adhesion at these elevated temperatures, the films can delaminate at the EMCM interface when seals are pulled before they are totally cooled.
In demanding packaging applications such as vertical form fill seal pouch packaging, where transverse heat seals are used, poor interlaminar bond strength will be manifested as a low hot tack value (below 2.0 Newtons/inch at 135° C.). The failure mode is typically one of delamination at the interface of the sealant layer and the EMCM layer, and/or the EMCM layer and the next adjacent (internal) layer.
A target hot tack value, which will represent a value typically minimally acceptable for many packaging applications, is at least 2.0 Newtons/inch at 135° C. Desirable values include from 2.0 to 10 Newtons/inch, such as 2.5 to 9.5 Newtons/inch, such as 3.0 to 9.0, 3.5 to 8.5, and 4 to 8 Newtons/inch at 135° C. Hot tack is measured in accordance with ASTM F 1921-98, which is incorporated herein by reference in its entirety. This ASTM test designates the use of either DTC or Theller instrumentation.